Amongst the prior art, it is known to use flexible metal bellows components as sealing elements for isolating fluids inside, or outside, the bellows. In such a case, each bellows may be referred to as a “seal,” due to the bellows being impervious to fluids.
It is also known that such metal bellows inherently have a degree of resilience, while defining a spring constant, and can be used in pressure-sensitive devices or spring-biasing environments in lieu of, for example a compressive coiled spring. Thus, while bellows can be used to provide the same spring bias as standard spring elements, bellows seals may provide the additional benefit of imposing a spring bias, while isolating fluids within certain regions, a benefit and function that standard spring elements, such as coiled springs, simply cannot provide. The advantages of these metal bellows seal assemblies can be utilized in many different fields of use.
For example, designers of automotive engines continue to face challenges associated with improving automotive emissions, while maintaining and improving internal combustion engine longevity, integrity and fuel efficiency. As a result, today's fuel systems in internal combustion engines, such as automotive engines, operate at higher pressures than those of similar fuel systems from the past. With higher pressure needs and tolerances, fuel pump components must meet greater performance demands.
Such fuel pumps typically have a plunger or piston that reciprocates to drive the movement of fuel from a fuel inlet, into a fuel collection region, and out to an engine fuel rail through a high pressure fuel outlet. The piston is typically positioned in the bore of the fuel pump, and powered by a separate driving system, such as a motorized revolving cam shaft and lobed cam. The pump's driving system is typically supplied with a lubricant, such as oil, to lubricate the biased, reciprocating fuel pump piston against friction and wear. Since the piston has a diameter that is slightly smaller than the diameter of the bore, it is often possible for small quantities of fuel to leak out of the fuel collection region, into the space between the piston and the bore, where it may then leak into the piston driving system, where it can contaminate the lubricant. Such contamination reduces the viscosity of the lubricant, thereby decreasing the lubricant's life and overall effectiveness, to affect the friction on the piston, as well as the piston's wear and fragmentation. Likewise, once fuel and the lubricant have mixed, small volumes of lubricant may travel on the outer surface of the piston, and be purged out through high pressure fuel outlet, into the fuel rail. When such oil-contaminated fuel undergoes the combustion process in the cylinders of an internal combustion engine, it can lead to undesirable engine performance and emissions problems.
Engine designers have begun to develop improved methods for avoiding this contamination and the commingling of fuel and lubricant, such as by providing a drain groove in the bore, where leaked fuel may be collected and diverted. However, such drain grooves may not fully prevent the contamination and commingling of fuel and lubricant. Further, that solution may also cause certain pressure spikes as the piston dilates under an axial load. Accordingly, in the fuel pump context, it would be desirable to provide a fuel pump that provides an improved seal towards preventing the commingling of fuel and lubricant.
More generally, it would be desirable to provide a bellows seal assembly configured to surround a reciprocating piston in any one of a number of machine operations, which seal assembly simultaneously serves as both a resilient spring member for applying a spring load within the machine, as well as a mechanism for sealing and isolating one or more fluids from within a separate region of the machine.